1. Field of the Invention
The present invention relates to manufacturing of a semiconductor laser, and more particularly, to an etching method for a multi-layered structure of semiconductors in groups III-V for manufacturing a surface emitting laser device (SEL), and a method of manufacturing a vertical cavity surface emitting laser device (VCSEL) using the etching method.
2. Description of the Related Art
Since an SEL has a low threshold current contrary to conventional edge-emitting laser diodes, and has a circular beam shape, the SEL has high optical fiber coupling efficiency and thus represents excellent device characteristics. Also, since the SEL is easy to manufacture as a device of a two-dimensional array, and can be tested while the SEL is still in a wafer state, the SEL has mass production characteristics of conventional electronic devices. Therefore, the SEL is currently under development as a promising device capable of replacing conventional optical devices in the fields of an optical communication network and optical sensors with its excellent performance and low manufacturing costs.
To manufacture the SEL, a mirror layer having high reflectance is required, and a material of high optical gain is required. Particularly, when a laser ray is used, different wavelengths should be used depending on applications, and accordingly, effective combination of materials should be considered according to respective wavelengths. For example, an SEL for a wavelength band 850 nm has been successfully commercialized by providing a GaAs substrate, a semiconductor mirror layer of high reflectance and an active layer of a high gain material using combination of GaAs/AlGaAs, and by providing excellent thermal characteristics.
However, in case of wavelength bands of 1.3 μm and 1.5 μm mainly used for communication, there is much difficulty in using the combination of GaAs/AlGaAs. Therefore, an InP substrate and one of InGaAsP or InAlGaAs are mainly used. However, in this case, growing of a large number of layers is required to obtain high reflectance. Also, quaternary materials such as InGaAsP and InAlGaAs have one tenth lower thermal conductivities than those of binary materials such as GaAs, that is, the quaternary materials have very low conductivities, which limits device characteristics.
Therefore, various methods have been proposed to overcome these problems and develop SELs for a long wavelength band. Particularly, many attempts have been made to solve a thermal characteristic deterioration problem raised when quaternary materials are used. For example, a technology has been proposed to use a mirror layer of InAlGaAs/InP instead of a conventional quaternary material InAlGaAs/InAlAs. This technology allows reducing a growth thickness using a relatively large refractive index difference and obtaining an excellent thermal characteristic from high thermal conductivity. However, even in this case, a dry etching process of a thickness of about 10 μm is still required to manufacture a desired device. When the dry etching process required herein is performed, a reaction gas in a Cl2—Ar group has been used as an etching gas in a related art. However, when this reaction gas is used, etching conditions are complicated and it is difficult to obtain a smooth etched surface after an etching process is completed. Particularly, InAlGaAs is effectively etched using a reaction gas in a Cl2—Ar group, but when InP is etched using a reaction gas in a Cl2—Ar group, a rough etched surface is obtained and etch stop may be generated by etching by-product. Accordingly, InP may be etched using a gas CH4—H2. However, when a gas CH4—H2 is used, an etching speed of InAlGaAs becomes too slow, which generates another problem. Also, an attempt has been made to use an etching gas where BCl3 is added to CH4—H2 in a related art, but BCl3 exists in a liquid state and thus it is difficult to deal with. Also, a separate apparatus for evaporating liquid state BCl3 is required in order to swiftly supply BCl3 into an etching chamber, which complicates a process equipment and increases manufacturing costs.